chore(backend): deprecation sweep — Pydantic V1 -> V2, utcnow -> tz-aware

Two low-risk Pydantic V1 idioms that will be hard errors in V3:
  - Query(regex=...) -> Query(pattern=...) (audit_routes, control_generator_routes)
  - class Config: from_attributes=True -> model_config = ConfigDict(...)
    in source_policy_router.py (schemas.py is intentionally skipped — it is
    the Phase 1 schema-split target and the ConfigDict conversion is most
    efficient to do during that split).

Naive -> aware datetime sweep across 47 files:
  - datetime.utcnow() -> datetime.now(timezone.utc)
  - default=datetime.utcnow -> default=lambda: datetime.now(timezone.utc)
  - onupdate=datetime.utcnow -> onupdate=lambda: datetime.now(timezone.utc)

All SQLAlchemy DateTime columns in the project already declare
timezone=True, so the DB schema expects aware datetimes. Before this
commit, the in-Python side was generating naive values and the driver
was silently coercing them. This is a latent-bug fix, not a behavior
change at the DB boundary.

Verified:
  - 173/173 pytest compliance/tests/ pass (same as baseline)
  - tests/contracts/test_openapi_baseline.py passes (360 paths,
    484 operations unchanged)
  - DeprecationWarning count dropped from 158 -> 35

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend-compliance/tests/test_isms_routes.py

@@ -13,7 +13,7 @@ Run with: cd backend-compliance && python3 -m pytest tests/test_isms_routes.py -
 import os
 import sys
 import pytest
-from datetime import date, datetime
+from datetime import date, datetime, timezone
 
 from fastapi import FastAPI
 from fastapi.testclient import TestClient
@@ -40,7 +40,7 @@ def _set_sqlite_pragma(dbapi_conn, connection_record):
     cursor = dbapi_conn.cursor()
     cursor.execute("PRAGMA foreign_keys=ON")
     cursor.close()
-    dbapi_conn.create_function("NOW", 0, lambda: datetime.utcnow().isoformat())
+    dbapi_conn.create_function("NOW", 0, lambda: datetime.now(timezone.utc).isoformat())
 
 
 app = FastAPI()